Field of the Disclosure
The present disclosure relates to a hydrotreating process to reduce the levels of contaminants in a contaminated diesel product. More specifically, the present disclosure relates to a hydrotreating process to remove sulfur from a diesel feed stream to produce ultra-low-sulfur-diesel (ULSD).
Description of Related Art
Global demand for diesel has risen quickly with increased growth of transportation fuels. At the same time, regulations on the properties of the transportation diesel have been established to substantially lower the sulfur levels in diesel fuels in order to reduce sulfur dioxide (SO2) emissions from use of such fuels. There are other pending rules calling to reduce the sulfur content in off-road diesel as well. European standards, for example, call for a sulfur content of less than 10 part per million by weight (wppm) which is often referred to as ultra-low-sulfur-diesel, or ULSD.
Hydrotreating processes, such as hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), which remove sulfur and nitrogen, respectively, have been used to treat hydrocarbon feeds to produce clean fuels. The processes can be conducted in various hydroprocessing units, such as three-phase hydroprocessing reactors or two-phase hydroprocessing reactors.
In a three-phase hydroprocessing reactor, commonly known as a trickle bed reactor, three phases (gas, liquid and solid) are present. The continuous phase through the reactor is the gas phase which is largely hydrogen. Therefore, a trickle bed reactor typically requires use of a large excess of hydrogen relative to the feed in order to form the continuous gaseous phase and effectively transfer hydrogen from the gaseous phase through a liquid-phase hydrocarbon feed to react with the feed at the surface of a solid catalyst. Excess hydrogen is recycled through a hydrogen recycle compressor to avoid loss of the hydrogen value.
Ackerson et al. in U.S. Pat. No. 6,123,835, disclose a two-phase hydroprocessing system which eliminates the need to transfer hydrogen from the vapor phase through a liquid phase hydrocarbon to the surface of a solid catalyst. In the two-phase hydroprocessing system, continuous phase through the reactor is the liquid phase, and a solvent, which may be a recycled portion of hydroprocessed liquid effluent, acts as diluent and is mixed with a hydrocarbon feed. Hydrogen is dissolved in the feed/diluent mixture to provide hydrogen in the liquid phase. Substantially all of the hydrogen required in the hydroprocessing reaction is available in solution.